A variety of techniques for achieving an effective usage of a mounting area by directly connecting a semiconductor chip that is not sealed in resin with a terminal electrode part on a circuit board using a bump have been developed in recent years. For example, according to a method of carrying out bump formation by using wire bonding, a semiconductor chip, or the like, and a terminal electrode part can be connected without fail.
In addition, according to a method for forming a bump on an electrode pad by printing solder paste, a bump can be simply formed so as to easily form the above described connection part.
In the above described wire bonding method, however, a bump is formed due to a complicated movement of a capillary and, therefore, formation requires a long period of time. In addition, the size of the bump electrode primarily depends on wire diameter and, therefore, it is necessary to utilize a wire of a small diameter in order to form a bump electrode of a small diameter that corresponds to a fine pitch of the terminal electrode part. Thus, the ratio of the cost of material for the wire of a small diameter to the cost of bump formation increases. Accordingly, when bump electrodes having many pins with a fine pitch are formed by using a wire bonding method, the cost of bump formation becomes very expensive because of low production efficiency as well as high material costs.
In addition, in the case of a method of forming a solder bump by printing solder paste, there are the demerits wherein instability in the supplied amount of solder paste, which is intrinsic to the printing system, can not be avoided and, moreover, cleaning is necessary after bump formation so that the cost of bump formation cannot be lowered.
Therefore, a bump formation method of a solderjet system that uses the nozzle shown in FIG. 17 is proposed as a new bump formation method. The principle that is conventionally adopted in an ink jet printer, or the like, is applied in this nozzle. Molten solder 108a is heated to the melting temperature, or higher, and is held in this nozzle 121 while an oscillator 122 is placed in the molten solder so that the direction of oscillation faces toward the microscopic aperture 121a. Referring to FIG. 17, whenever an oscillation is applied to the molten solder l08a by means of the oscillator 122, one molten solder drop 108 is discharged from the microscopic aperture 121a of the nozzle. This solder drop is discharged toward an electrode pad on a work piece (substrate, semiconductor chip, or the like) so that a bump joined to the electrode pad is formed. According to this bump formation method having a solder jet system, solder bumps can be formed effectively, simply, and at a low cost.
As shown in FIGS. 18A and 18B, however, there is a case where a microscopic solder drop 109 suddenly and unexpectedly occurs together with an intended solder drop at the stage where the molten solder is discharged from the microscopic aperture 121 a of the nozzle as a predetermined molten solder drop 108. This microscopic solder drop is called a satellite and tends to start occurring after the nozzle has started to be utilized and a predetermined period of time has elapsed. Satellites 109 fly to, and attach to, a substrate that is a work piece, in particular, to the vicinity of an electrode pad.
Here, a solder bump formation method of a solder jet system according to a prior art is described below. Herein, a case where the work piece is a substrate is described. First, as shown in FIG. 19, an electrode pad 102 made of aluminum is formed on the substrate 101. A gold film is used for a layer that the solder bump contacts and a plurality of barrier layers are provided between the two so that the electrode pad and the gold film do not react with each other. First, as shown in FIG. 20, a mask 103 with an aperture is formed so as to correspond to a region of this electrode pad. This mask 103 can be fabricated through a photomechanical process. Next, as shown in FIG. 21, a titanium film 105 is formed on the electrode pad 102 by sputtering through the aperture of the mask 103. Next, a nickel film 106 is formed by sputtering in the same manner on the titanium film 105 (FIG. 22). The titanium film 105 and the nickel film 106 form barrier layers. A gold film 107 that is a connection layer contacting a solder bump is formed on these barrier layers (FIG. 23). After this, mask 103 is removed and a solder bump 108, shown in FIG. 24, is formed by using the above described nozzle of the solder jet system. At this time, as shown in FIG. 18B, satellites 109, in addition to the solder drop 108, occur and satellites 109 attach to the substrate 101 in the vicinity of the electrode pad 102 on the substrate. The satellites that have attached in the vicinity of the electrode pad may possibly bridge the electrode pads causing a malfunction or allowing a disadvantageous phenomenon to occur. It is necessary to remove these satellites in order to provide a high quality semiconductor device w he rein no problem occurs with respect to the reliability of the electrical connection.